1. Field of the Invention
This invention relates generally to angioplasty radiation therapy apparatus and methods, and more particularly to a surgical apparatus and method for reducing restenosis after angioplasty utilizing beta radiation and a catheter with a stainless steel guide wire having a beta emitting radiation source at the distal end.
2. Description of Prior Art
Restenosis is a type of wound in the process of healing and is the resultant of two components, artery constriction and internal hyperplasia. It has been proven that radiation can limit the hyperplasia component by killing the proliferating cells. The use of radioactive stents has shown effective results to eliminate or at least to reduce the intimal hyperplasia usually expressed as the ratio between the area of the artery to the fracture length.
The use of a stent with a gamma radiation source such as iridiuim-192 has been a first step in the development of a procedure to irradiate the area of the vessel under consideration. Typically, gamma sources using iridium-192 have been used to irradiate the arteries under a continuous or intermittent condition with different results. The source is implanted using a stent and the combination of the mechanical effect (stent is expanded using a balloon) together with the radiation level of the source, has been proven to be beneficial in reducing the restenosis as shown by angiography and ultrasound analysis. The rate of irradiation under which the vessel is targeted is very important since several experiments indicate that absorbed doses below 8 Grays may dramatically affect the results.
The use of a stent with a gamma radiation source may also present several problems. The stents carrying the radioactive source can create uncomfortable situations since they are designed to reside permanently in the area under treatment. The use of a gamma source has also proven to be not strong enough to deliver the minimum absorbed doses without affecting other organs because of its longer range.
Other known radioactive stent methods and apparatus involve the use of a seed-shaped radioisotope or xe2x80x9cseedxe2x80x9d mechanically attached to the guide wire or to the stent as the source of gamma or beta radiation.
The present invention is distinguished over the prior art, in general, by a radiation therapy apparatus and method for significantly reducing or preventing restenosis after angioplasty that utilizes beta radiation and a catheter with a stainless steel guide wire having a beta emitting radiation source at the distal end.
The present invention utilizes a physical vapor deposition process (PVD) to ionically bond a phosphorus target material directly to the surface of the guide wire to form a unitary structure without any mechanical joint or attachment in such a way that the wire itself will become the carrier and the holder of the source for the radiation therapy. The wire material to be coated is enclosed in a vacuum chamber where the temperature is raised. The deposition material (phosphorus) is vaporized by an electric arc. The phosphorus ions are mixed with a nitrogen gas to form a plasma. A negative charge is applied to the section of wire to be coated, and a high positive charge is applied to the plasma. These opposite charges of the plasma and the base material of the guide wire ionically bonds a firm and hard phosphorus film coating on the surface of the wire to form a unitary structure.
In this way the target (phosphorus) is bonded into the area of the guide wire which is then activated by neutrons using a high flux research reactor unit until the desired activation is reached.
The radiation therapy guide wire is similar in size, shape, and flexibility to the conventional guide wire used for the angioplasty procedure, and the cardiologist merely needs to remove the conventional guide wire after completion of the angioplasty procedure and introduce, using the same catheter, the radiation therapy wire of the present invention to carry out the radiation therapy procedure described herein.
In a preferred embodiment, the particular physical vapor deposition process (PVD) used to form the present radiation therapy wire is described in greater detail in a publication entitled xe2x80x9cHandbook of Physical Vapor Deposition Processingxe2x80x9d, by Donald M. Mattox, Noyes Publications, 1998 ISBN 0-8155-1422-0.
It is therefore an object of the present invention to provide a minimumly invasive radiation therapy procedure using a beta radiation source that will substantially reduce or prevent restenosis after balloon angioplasty and adds only approximately 20 minutes to the coronary angioplasty procedure.
It is another object of this invention to provide a radiation therapy guide wire having a beta emitting radiation source at the distal end formed by physical vapor deposition (PVD) that ionically bonds the beta radiation target material (phosphorus) to the base material of the wire to form a unitary structure and eliminates the need for a permanently activated stent and mechanical attachments or xe2x80x9cseedsxe2x80x9d having limited area/volume available for neutron activation.
Another object of this invention is to provide a radiation therapy guide wire having a beta emitting radiation source ionically bonded at the distal end by physical vapor deposition (PVD) that allows a cardiologist to reach smaller or angulated areas during a radiation therapy procedure.
Another object of this invention is to provide a radiation therapy guide wire having a beta emitting radiation source such as phosphorus-32 ionically bonded at the distal end that has a shorter energy range than gamma radiation thereby minimizing damage to other organs.
A further object of this invention is to provide a radiation therapy guide wire having a beta emitting radiation source such as phosphorus-32 ionically bonded at the distal end which is not restricted to the small area/volume of a seed, allows higher activation of the source, and allows it to exceed a minimum threshold of 8 Grays of absorbed dose to validate the procedure.
A still further object of this invention is to provide a radiation therapy guide wire having a beta emitting radiation source bonded at the distal end which does not utilize a seed and is sized to allow radiation therapy procedures using the same catheter delivery system that is used for the angioplasty procedure.
Other objects of the invention will become apparent from time to time throughout the specification and claims as hereinafter related.
The above noted objects and other objects of the invention are accomplished by a radiation therapy apparatus and method for significantly reducing or preventing restenosis after angioplasty which utilizes a stainless steel guide wire having a phosphorus beta emitting radiation source ionically bonded thereon at its distal end to form a unitary structure. The radiation therapy wire is similar in size, shape, and flexibility to the conventional guide wire used for the angioplasty procedure, and is introduced using the same catheter to carry lout the radiation therapy procedure. When the beta emitting source reaches the critical section in a vessel or artery, a protective sleeve is retracted and the radiation source is exposed to the damaged area for a sufficient amount of time for the vessel to absorb the required dosage. Because the range of beta radiation is much lower than gamma radiation, the risk of radiation damage to other areas is minimal. Since the half life of the P-32 is 14 days and the required absorbed dose should be at least 8 Gy, an initial activation of at least 14 mCi is recommended.